Sky and Telescope - November 2015 - 63

Alan Dyer
Use these techniques to create stunning movies of
the sky turning above scenic landscapes.
In the days of ﬁlm, only a handful of cinematographers
attempted time-lapse photography of the night sky. To
do it, they had to use extremely expensive, custom-made
movie cameras. Today, the digital single-lens reﬂex
(DSLR) camera has democratized time-lapse shooting,
making it possible for anyone to create movies with up
to IMAX-grade resolution. Success, though, comes from
knowing some useful techniques.
If you followed my article in the October issue,
chances are you're already well on your way to creating
your own nightscape movie. Here are some tips to help
you plan your time-lapse movie and bring it all together.

Focus and Compose
The hours you can spend shooting a time-lapse sequence
will be for naught if all your images are out of focus.
Use Live View (or Live Focus) to focus manually on a
bright star or distant light. Then take test shots to get the
framing right. Good composition is just as important at
night as it is during the day. Time-lapse sequences also
require that you compose not only for how the sky looks
now, but how it will look an hour or more later when the
sequence ends. Use planetarium software to illustrate
how photogenic sky subjects such as Orion or the Milky
Way will move during your shoot.

Exposures and Intervals
Just as with shooting nightscapes, the best exposure in a
time-lapse sequence is whatever produces a well-exposed
image for each frame. Underexpose and you'll introduce
noise and ugly artifacts in the shadows.
However, time-lapses are made of hundreds of
frames. To keep the time it takes to acquire all those
frames to a reasonable length, you often need to restrict

exposure to no longer than 30 seconds. That, in turn,
might require shooting at a higher ISO speed (3200 to
6400) or wider aperture (f/2) than you might choose for
a single-shot nightscape.
But what should the interval be? That depends on
what your equipment's deﬁnition of interval is. Setting
the interval can be confusing, as some intervalometers
(notably Canon's TC-80N3) deﬁne "interval" to mean
the time from when the shutter closes to when it opens
again. In that case, set INT to no more than 1 to 5 seconds, assuming you are also using the intervalometer to
set the exposure, with the camera itself on Bulb. Make
the interval longer than a few seconds and the stars will
jump across the sky.
However, many control devices deﬁne interval to
mean the time from when the shutter opens to when it
opens again for the next shot. In that case, set what the
device calls interval to a value 1 to 5 seconds longer than
whatever exposure time you are using. If you change
your exposure time, you'll need to change the interval
as well. Forget to do that and the device might try to ﬁre
the shutter while the camera is still taking an exposure,
resulting in missed frames and gaps in the sequence, an
error called "frame collision."
How many frames should you take? As another rule
of thumb, plan to play back the ﬁnal movie at 30 frames
per second. This produces the smoothest motion. So for
a clip that lasts 10 seconds on screen you will need to
shoot 30 × 10 = 300 frames. You can shoot fewer frames,
but the clip won't last as long.

MOTION PICTURES Facing page: While time-lapse photography can involve the use of specialized motion-control gear, such
as the Dynamic Perception dolly unit in use at left here, eﬀective
sequences are possible with no more than a camera on a ﬁxed
tripod, at right. All images are courtesy of the author.
TIME-LAPSE GEAR Right: Besides a tripod, a fast wide-angle
lens and a reliable intervalometer are the most important timelapse accessories. While camera batteries can last for 2 to 4
hours of continuous shooting, have an extra battery on hand to
swap in mid-shoot if needed.

Sk yandTelescope.com November 2015

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Sky and Telescope - November 2015

Table of Contents for the Digital Edition of Sky and Telescope - November 2015